Conventionally, solid-state imaging elements such as a CMOS (Complementary Metal Oxide Semiconductor) image sensor have been widely used for imaging apparatuses. The imaging apparatus of this type has an AF (Autofocus) function of automating focusing. In recent years, requirements for AF accuracy and AF speed of a subject are increased more and more.
For example, in general, an AF module is additionally incorporated in a digital single-lens reflex camera. It involves an increase in casing size and mounting cost. Therefore, some of mirrorless interchangeable-lens cameras and compact digital still cameras realize the AF function by contrast AF without the additionally incorporated AF module. However, it is difficult to say that the AF speed is sufficient in current state.
Therefore, a digital camera that increases the AF speed by incorporating phase-difference pixels in a solid-state imaging element and realizing the AF function by image surface phase difference AF has been in practical use. In general, in the image surface phase difference method, a phase-difference pixel A and a phase-difference pixel B are paired for realizing the AF function. As a method of improving the AF accuracy, it is effective to increase the number of phase-difference pixels that are incorporated in the solid-state imaging element. Conventionally, it is realized by setting the phase-difference pixels A and B to be the same size as a normal pixel for imaging and, for example, changing a metal light shield.
Furthermore, Patent Document 1 discloses a technology in which phase-difference pixels A and B are placed in one pixel for increasing the number of pixels for AF, to thereby improve the AF accuracy. In addition, Patent Document 2 discloses a technology relating to back side illumination type phase-difference pixels.
Patent Document 1: Japanese Patent Application Laid-open No. 2012-165070
Patent Document 2: Japanese Patent Application Laid-open No. 2012-84816